Apparatus for electrostatically spraying paint



July 19, 1960 o. GENGENBACH ET AL 2,945,472

APPARATUS FOR ELECTROSTATICALLY SPRAYING PAINT Filed Jan. 23, 1956PRESSURE-ADJUSTA BLE INVENTORS OTTO, GENGEN BACH HORST SCHENE ATTORNEYSAPPARATUS FOR ELECTROSTATICALLY SPRAYING PAINT btto Gengenbach and HorstSchene, Sindelfingen, Kreis Bohlingen, Germany, assignors toDaimler-Benz Aktiengesellschaft, Stuttgart-Unterturkheim, Germany FiledJan. 23, 1956, Ser. No. 560,825

Claims priority, application Germany Feb. 9, 1955 Claims. (Cl. 118-626)The present invention relates to a process and apparatus for coatingobjects with a liquid, and more particularly to a process and apparatusfor electrostatically spraying paint.

The known processes exhibit the disadvantage that the paint to besprayed can be applied to large surfaces only in a relatively unevenmanner. This may be attributed to the fact that the spray-paint in theprior art devices leaves a nozzle or similar device under pressure outof a plurality of small bores from which it is usually discharged in theform of a cone or fan.

'With other known processes this disadvantage is sought to be avoided inthat the paint to be sprayed is sucked or drawn off electrostaticallyfrom a stationary liquid surface. However, with this process thespray-paint can be applied or sprayed only in a horizontal direction sothat objects with large surfaces to be sprayed have to be guided ormoved past the stream of paint spray in a vertical direction. However,such a flow or movement of the material and goods is inappropriate inconnection with modern production methods which are based on horizontalassembly lines.

Accordingly, it is an object of the present invention to provide aprocess and apparatus for carrying out the process which obviates allthese disadvantages of the prior art.

It is another object of the present invention to provide a process andapparatus enabling the spraying of paint onto large surfaces in a veryeven manner.

A still further object of the present invention resides in anarrangement which permits the undercoating of large surfaces in a veryeven manner by electrostatically spraying the coating onto these largesurfaces.

Another object of the present invention lies in the realization of acoating process, such as a paint-spraying process, which is suitable forassembly lines moving in essentially horizontal planes.

It is a still further object of the present invention to provide aninstallation for carrying out an improved electrostatic spraying processin which the coating material such as paint, is circulated underpressure and to provide a nozzle particularly appropriate for use insuch installations.

Another object of the present invention lies in the use of anelectrostatic field for drawing off the fluid to be sprayed which issubjected to a capillary action at the place where its electrostaticdischarge occurs and to return to the circulatory system any excessfluid not drawn off electrostatically during the spraying action.

Still another object of the present invention resides in providing anelectrostatic spraying system in which a narrow longitudinal gapexerting a capillary action on the fluid is used as a nozzle and inwhich the fluid is circulated under such a pressure that in the absenceof and electrostatic field of predetermined strength the fluid merelyflows over out of the gap but is not subjected to any discharge action.

" The present invention avoids the disadvantages of the prior art inthat the liquid such as paint to be sprayed which, for example, iscontinuously circulated by means of a pump, leaves through a narrowlongitudinal gap out of which the electrostatic suction takes place.More paint is ordinarily supplied through the gap by appropriateadjustment than is drawn oif electrostatically and the excess portion ofthe paint which is not drawn ofl? electrostatically for purposes ofspray-painting passes over into a collecting container.

The present invention further relates to an installation and apparatusfor carrying out the process.

The apparatus consists of two concentrically arranged pipe or tubesections open only on one side thereof, of which the inner pipe sectionserves as supply line for the spray-paint and the open gap of whichserves as spray nozzle while the outer pipe section forms thereturn linefor the excess paint which has flown over out of the gap.

Further objects, features and advantages of the pres ent invention willbecome more obvious from the following description when taken inconnection with the accompanying drawing which shows, for purposes ofillustration only, one embodiment in accordance with the presentinvention, and wherein Figure 1 illustrates schematically a sprayinginstallation in accordance'with the present invention;

Figure 2 is a perspective view through a section of the spray nozzledrawn approximately in its actual size, showing that end portion of thenozzle as seen at the left of the section line IIII of Figure 3; and

Figure 3 is a longitudinal section of the spray nozzle with the arrowsindicating the path of non-sprayed liquid over-flow.

Referring now more particularly to the drawings wherein like referencenumerals are used throughout the various views to designate like parts,reference numeral 6 designates a container for the paint. The paint iscontinuously supplied from the container 6 by means of a pump 5 throughthe feed or supply line 5a to the inner line or tube section 4 of thespray nozzle 3. ject 8 which may be supported from a transporting device7, which at the same time serves as conductor, passes past or over thespray nozzle 3, the particles of the paint are subjected to theinfluence of an electric high voltage field which is maintained betweenthe supply nozzle 3 connected through line 13, for example, to thepositive terminal of an appropriate power supply or high voltage sourceand the goods or objects 8 which are connected with the negativeterminal of the power supply through the conductor formed by thetransporting device 7 and which serve as opposite pole of theelectrostatic field. If so desired, the negative terminal of the highvoltage generator HV may be connected to ground so that each object orarticle 8 passing the nozzle 3 constitutes a grounded mass as regardsthe electrostatic field. e

The actual mode of operation in the spray nozzle 3 will now be explainedwith reference to Figure 2. The

paint to be sprayed flows under the pressure caused by the pump 5through the cross section 9 of the pipe 4 and leaves the same throughthe gap 10; The width However, the overall cross section of the gapformedbetween wall portions 4 and 4" and the pressure caused by thecirculation pump 5 are so selected and adjusted with respect to eachother that the paint to be sprayed would not be subjected to anyspraying action out of If an obgap without the presence of an electricfield of predetermined strength but would merely flow over. -'Ihe thusover-flowing paint is caught in the gaps 10a which are formed by theessentially straight, parallel wall portions 11', 11" extending parallelto and on the outside of both wall portions 4' and 4" and is thereuponreturned through the annular channel 12 formed between the con centricWalls of the pipe section 4 and of the pipe section 11 into thecirculatory system in any suitable manner, illustrated schematicallyonly in Figure 1 in which the excess paint is permitted to flow backinto the container 6.

During the spraying operation which occurs with the passage of theobject 8 the paint is drawn 01f under the effect of the electric highvoltage field to thereby prQ hre a Sp y ng r atc ing t on om he edges ofthe gap 10 to the objects or goods filwhich are to be coated with thepaint.

The process and the described installation in accordance with thepresent invention ofier the advantage. with respect to those of theprior art that a surface like spray discharge of very great evenness isproduced thereby.

The illustrated arrangement is particularly appropriate if objects withlarge surfaces are to be sprayed from the undersides thereof. However,with an inclined arrangement of the, spray nozzle vertical surfaces mayalso be sprayed.

The liquid used in connection with the present invention may be anysuitable paint or other liquid coating material the even application ofwhich to surfaces, particularly large surfaces, is desired.

It is understood that one end of the cross section 9 of nozzle 3, forexample, the one not visible in Figure 2,

is closed in any suitable manner, while the other end is connected withthe supply line 5a.

While we have shown and described one specific embodiment of ourinvention it is understood that the same is susceptible of many changesand modifications without departing from the spirit and scope of ourinvention, and we intend to cover all such changes and modificationsexcept as defined by the appended claims.

We claim:

1. An apparatus for electrostatically spraying objects comprising supplymeans ofpaint, paint spray means con nected to said supply meansincluding a nozzle, means for continuously circulating said paint underpressure from said supply to said paint spray means and back to. saidsupply means, said nozzle. being formed by two rela tively fixedelongated concentric members of which the inner member has a laterallyexposed liquid discharge gap and forms the discharge nozzle and theouter memher an over-flow channel, said circulating means including aliquid supply line connected to one end of said inner member, said innermember being so constructed that substantially all of the liquidsupplied thereto discharged through said gap, said inner member havingclosely spaced Walls defining said discharge gap with at least one ofthe walls having an electrically conducting edge, and means forestablishing an electrostatic fieldin,

the region of said nozzle between said edge and an object to be coatedto produce a spray discharge of said paint from the edge of the Walls ofsaid inner member forms aid p- 2. The apparatus according to claim 1,wherein said liquid, through said spray means. to saidnozzle, saidnozzle,

comprising an elongated liquid carrying line having a narrownpwardlydirected longitudinal liquiddispha rge.

therein, and a channel structure at least partiallysurrounding said lineto receive liquid overflow from said gap, said liquid carrying linebeing so constructed as to discharge liquid therefrom primarily onlythrough said gap, and means electrically connected to an electricallyconducting portion of said nozzle extending along the edge of said gapfor establishing an electrostatic high voltage field within the area ofsaid nozzle to produce a spray discharge of liquid therefrom to anobject being sprayed.

4. An apparatus for electrostatically spraying objects with a liquid,comprising spray means including a nozzle, means for continuouslycirculating liquid through said spray means to said nozzle, said nozzlecomprising a line with an upwardly directed elongated liquid dischargegap and a channel structure fixed relative said line to receive liquidoverflow from the gap, means for returning said liquid overflow fromsaid channel to said circulating means, and means electrically connectedto a portion of said nozzle defining an edge of said gap forestablishing an electrostatic high voltage field within the rea of saidnozzle to produce a spray discharge of liquid from said gap to an objectbeing sprayed.

5,. An apparatus for electrostatically spraying objects with a liquidcomprising a source for supplying said liquid, spray means including anelongated nozzle, said nozzle comprising a tube-like structure connectedto said liquid supply source for receiving liquid therefrom under slightpresusre, said tube-like structure having an elongated upwardly directedgap for discharging liquid therefrom, said structure being soconstructed that substantially all of the liquid passing therethrough isdischarged from said gap, said gap being defined by closely spaced wallsat least one of which is provided with an electrically conducting edgeextending longitudinally of said gap, said nozzle further comprising achannel structure at least partially surrounding said tube-likestructure and extending at least the length of the latter to receiveliquid overflow from the gap, and means for establishing anelectrostatic high voltage field within the area of said nozzle betweensaid edge and an object to be sprayed to produce a spray discharge ofliquid upon the latter.

6. An apparatus for electrostatically spraying objects with a liquidcomprising a source for supplying said liquid, spray means including anelongated nozzle, said nozzle comprising a tube-like structure connectedto said liquid supply source for receiving liquid therefrom under slightpressure, said tube-like structure having an elongated upwardly directedgap for discharging liquid therefrom, said structure being soconstructed that substantially'all of the liquid passing therethrough isdischarged from said gap, said gap being defined by closely spaced wallsat least one of which is provided with an electrically conducting edgeextending longitudinally of said gap, said nozzle further comprising achannel structure at least partially surrounding said tube-likestructure and extending at least the length of the latter to receiveliquid overflow from the gap, and means for establishing anelectrostatic high voltage field within the area of said nozzle betweensaid edge and an object to be sprayed to produce a spray discharge ofliquid upon the latter, said liquid source including means foradjustingthe pres sure of said liquid supply with respect to the rate ofliquid flow through said gap and the strength of said electrostaticfield so thatin theabsence, of said. field said liquid will only flowover the edge ofv said, gap into said channel structure without beingdischarged as, a, spray from said nozzle.

7. An apparatus. for. electrostatically spraying objects.

with a, liquid, comprising a source for supplying. said liquid,, Spraymeans, including an elongated, nozzle, said.

tially all of the liquid passing therethrough is discharged from saidgap, said gap being defined by closely spaced walls at least one ofwhich is provided with an electrically conducting edge extendinglongitudinally of said gap, said nozzle further comprising a channelstructure at least partially surrounding said tube-like structure andextending at least the length of the latter to receive liquid overflowfrom the gap, means for establishing an electrostatic high volatge fieldwithin the area of said nozzle between said edge and an object to besprayed to produce a spray discharge of liquid upon the latter, andmeans for continuously circulating said liquid from said supply sourcethrough said nozzle and back to said source producing only overflow ofsaid liquid from said gap in the absence of said electrostatic field.

8. An electrostatic spray apparatus comprising two telescoped tube-likemembers each having a longitudinally extending gap defined by spacedwall portions, the wall portions of the inner of said structures beingclosely spaced and extending outwardly between the wall portionsdefining the gap of said outer tube, said inner structure being closedto prevent discharge of said liquid therefrom except at said gap, meansconnected with said inner structure to supply liquid thereto, at leastthe portion of said inner structure extending longitudinally of said gapat the edge thereof being electrically conducting, and means forestablishing an electrostatic high voltage field between theelectrically conducting portion of said nozzle and an object disposed infront of said dis- 6 charge gap for producing a spray discharge ofliquid upon said object, the walls of said outer tube-like structubebeing so positioned relative said inner structure as to receive overflowliquid from said gap and conduct said overflow liquid longitudinally ofsaid nozzle.

9. An electrostatic spray apparatus according to claim 8, wherein thewalls of said inner tube defining the discharge gap are closely spacedso that the liquid is distributed therebetween at least partially bycapillary action.

10. An electrostatic spray apparatus according to claim 8, includingmeans for receiving the overflow liquid from said outer structure andrecirculating the overflow liquid to said liquid supply means.

References Cited in the file of this patent UNITED STATES PATENTS1,416,929 Bailey May 23, 1922 1,641,403 Van Derhoef Sept. 6, 19271,968,687 Johnson July 31, 1934 2,111,761 Eckert Mar. 22, 1938 2,309,981Randall Feb. 2, 1943 2,394,656 Beregh Feb. 12, 1946 2,658,009 RausburgNov. 3, 1953 2,685,536 Starkey et al Aug. 3, 1954 2,781,279 Miller Feb.12, 1957 2,784,114 Miller Mar. 5, 1957 FOREIGN PATENTS 518,820 CanadaNov. 22, 1955

